Rig baking

ABSTRACT

Model components can be used to pose character models to create a variety of realistic and artistic effects. An embodiment of the invention analyzes the behavior of a model component to determine a statistical representation of the model component that closely approximates the output of the model component. As the statistical representation of model components execute faster than the original model components, the model components used to pose a character model can be replaced at animation time by equivalent statistical representations of model components to improve animation performance. The statistical representation of the model component is derived from an analysis of the character model manipulated through a set of representative training poses. The statistical representation of the model component is comprised of a weighted combination of posed frame positions added to a set of posing errors controlled by nonlinear combinations of the animation variables.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application claims priority to and incorporates by reference forall purposes U.S. Provisional Patent Applications “Rig Baking,” Ser. No.60/470,590, and “Defrobulation,” Ser. No. 60/470,767, both filed May 14,2003. This application further incorporates by reference for allpurposes U.S. patent application “Defrobulated Angles for CharacterJoint Representation,” filed Ser. No. 10/844,049.

BACKGROUND OF THE INVENTION

The present invention relates to the field of computer graphics, and inparticular to methods and apparatus for animating computer generatedcharacters. The present invention relates to the field of computergraphics. Many computer graphic images are created by mathematicallymodeling the interaction of light with a three dimensional scene from agiven viewpoint. This process, called rendering, generates atwo-dimensional image of the scene from the given viewpoint, and isanalogous to taking a photograph of a real-world scene. Animatedsequences can be created by rendering a sequence of images of a scene asthe scene is gradually changed over time. A great deal of effort hasbeen devoted to making realistic looking rendered images and animations.

Computer-generated animation of characters is accomplished bymanipulating a three-dimensional model of a character into a series ofbodily positions, or poses, over a sequence of frames. A realisticlooking character model is often extremely complex, having millions ofsurface elements and hundreds or thousands of attributes. Due to thecomplexity involved with animating such complex models, animation toolsoften rely on armatures and animation variables to define characteranimation.

An armature is a “stick figure” representing the character's pose, orbodily position. By moving the armature segments, which are the “sticks”of the “stick figure,” the armature can be manipulated into a desiredpose. As the armature is posed by the animator, the animation toolsmodify character model so that the bodily attitude of the characterroughly mirrors that of the armature.

Animation variables are another way of defining the character animationof a complex character model. Animation variables are parameters forfunctions that modify the appearance of a character model. Animationvariables and their associated functions are used to abstractcomplicated modifications to a character model to a relatively simplecontrol. Animation variables and their associated functions maymanipulate armature segments, thereby altering the appearance of thecharacter model indirectly, or manipulate the character model directly,bypassing the armature.

For example, a single animation variable can define the degree ofopening of a character's mouth. In this example, the value of theanimation variable may manipulate several different parts of thearmature and/or modify portions of the character model directly tocreate a modified character model having a mouth opened to the desireddegree.

The functions associated with animation variables, referred to as modelcomponents, can be used to create a variety of realistic and artisticeffects. For example, model components can be used to create layers ofbones, muscle, and fat beneath the surface of a character model, so thatthe surface or skin of a character model deforms realistically as it isposed. Model components can also be used to simulate the movement ofnon-rigid features such as hair and cloth. In addition to replicatingspecific physical phenomena, model components can be used to manipulatethe character model according to an algorithm or procedure, such assculpted shapes, metaballs, and physics simulations.

Model components can be extremely complex and therefore time-consumingto execute. To create artistically effective character animation, ananimator often creates a rough version of a scene and then repeatedlyfine-tunes the character animation to create desired drama andexpression of the final scene. The time needed to execute modelcomponents as animators pose and repose character models hinders theefficiency of the animator. In the worst case, an animator may be forcedto use simplified “stand-in” character models to create the initialanimation, and then wait to see the resulting animation with the finalcharacter model. In this situation, the animator is essentially workingblind and can only guess at the final result. Conversely, the additionalcomputing resources needed to process model components in a reasonabletime, if even possible, substantially increases the costs of creatinganimation.

It is therefore desirable for a system and method of optimizing theperformance of model components such that they can be executed in areasonable time without consuming undue computing resources. It isfurther desirable to be able to optimize any type of model component,regardless of its function or complexity.

BRIEF SUMMARY OF THE INVENTION

Model components can be used to pose character models to create avariety of realistic and artistic effects. An embodiment of theinvention analyzes the behavior of a model component to determine astatistical representation of the model component that closelyapproximates the output of the model component. As the statisticalrepresentation of model components execute faster than the originalmodel components, the model components used to pose a character modelcan be replaced at animation time by equivalent statisticalrepresentations of model components to improve animation performance.The statistical representation of the model component is derived from ananalysis of the character model manipulated through a set ofrepresentative training poses. The statistical representation of themodel component is comprised of a weighted combination of posed framepositions added to a set of posing errors controlled by nonlinearcombinations of the animation variables.

In an embodiment of the invention, a method of manipulating at least aportion of a character model into a pose using a model componentcomprises creating a statistical representation, referred to as a bakedcomponent, from the model component. The method identifies a portion ofthe character model associated with the baked component and determines aset of geometrically posed positions of a set of points of the charactermodel from the pose. The method also predicts a set of posing errorsassociated with the set of points of the character model from the bakedcomponent and the pose. Each of the set of posing errors specifies adisplacement of a point from a geometrically posed position. Themanipulated character model is then formed by applying the set of posingerrors to the set of geometrically posed positions of the set of points.

In an additional embodiment, the portion of the character modelassociated with the pose is identified by at least one reference frameinfluencing the portion of the character model. Furthermore, anembodiment defines the pose at least in part by a set of animationvariables. In yet a further embodiment, animation variables, such asjoint rotation angles, are expressed in a defrobulated form.Additionally, the set of posing errors may specify a single displacementof a point or a series of displacements of a point from a geometricallyposed position over time.

In another embodiment, the baked component is created from the modelcomponent by identifying at least a portion of the character modelassociated with the model component. This embodiment then manipulatesthe character model through each of a set of training poses. The set oftraining poses are defined by a set of inputs and are representative ofa range of motion of the character model. From the set of trainingposes, the embodiment determines a set of training posing errors for atleast one point of the character model and then analyzes the set oftraining posing errors to determine a relationship between the set ofinputs and the set of training posing errors. In yet a furtherembodiment, analyzing the set of posing errors includes performing aregression analysis of the set of training posing errors against the setof inputs.

In a further embodiment of creating a baked component, the set of inputsincludes a set of animation variables. A portion of the set of animationvariables are joint rotation angles expressed in a defrobulated form.Additionally, each of the set of training posing errors is at least onedifference in position of the point of a character model from ageometrically posed position to at least one position specified by themodel component. Each of the set of posing errors may specify a singledisplacement of a point or a series of differences in position over timeof the point of the character model from the geometrically posedposition to a set of positions over time specified by the modelcomponent.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described with reference to the drawings, inwhich:

FIG. 1 illustrates a block diagram of a computer system suitable forimplementing an embodiment of the invention;

FIG. 2 illustrates a prior use of model components to determine theposed position of points on an articulated character model;

FIG. 3 illustrates the use of baked components to determine the posedposition of a point on an articulated character model according to anembodiment of the invention;

FIG. 4 illustrates two phases of a method for creating a posed charactermodel according to the embodiment of the invention;

FIG. 5 illustrates a method for creating a baked component from a modelcomponent associated with an articulated character model according to anembodiment of the invention;

FIGS. 6A–6C illustrate an example application of a method for creating abaked component from a model component associated with an examplearticulated character model according to an embodiment of the invention;

FIG. 7 illustrates a method for determining the posed position of apoint on an articulated character model from a baked component accordingto an embodiment of the invention; and

FIGS. 8A–8C illustrate an example application of a method fordetermining the posed position of a point on an articulated charactermodel from a baked component according to an embodiment of theinvention.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 illustrates a block diagram of a computer system suitable forimplementing an embodiment of the invention. FIG. 1 illustrates anexample computer system 100 capable of implementing an embodiment of theinvention. Computer system 100 typically includes a monitor 110,computer 120, a keyboard 130, a user input device 140, and a networkinterface 150. User input device 140 includes a computer mouse, atrackball, a track pad, graphics tablet, touch screen, and/or otherwired or wireless input devices that allow a user to create or selectgraphics, objects, icons, and/or text appearing on the monitor 110.Embodiments of network interface 150 typically provides wired orwireless communication with an electronic communications network, suchas a local area network, a wide area network, for example the Internet,and/or virtual networks, for example a virtual private network (VPN).

Computer 120 typically includes components such as one or more generalpurpose processors 160, and memory storage devices, such as a randomaccess memory (RAM) 170, disk drives 180, and system bus 190interconnecting the above components. RAM 170 and disk drive 180 areexamples of tangible media for storage of data, audio/video files,computer programs, applet interpreters or compilers, virtual machines,embodiments of the herein described invention including geometric scenedata, object data files, shader descriptors, a rendering engine, outputimage files, texture maps, and displacement maps. Further embodiments ofcomputer 120 can include specialized audio and video subsystems forprocessing and outputting audio and graphics data. Other types oftangible media include floppy disks; removable hard disks; opticalstorage media such as DVD-ROM, CD-ROM, and bar codes; non-volatilememory devices such as flash memories; read-only-memories (ROMS);battery-backed volatile memories; and networked storage devices.

FIG. 2 illustrates a prior use of model components to determine theposed position of example points on an articulated character model 200.FIG. 2 illustrates a portion of the shoulder and arm region of charactermodel 200. In an embodiment, character model 200 is a three-dimensionalcomputer model of an object, although it is shown in two dimensions inthe figures for clarity. Additionally, although character model 200 isshown to be humanoid in shape, character model 200 may take the form ofany sort of object, including plants, animals, and inanimate objectswith realistic and/or anthropomorphic attributes.

Character model 200 can be created in any manner used to createthree-dimensional computer models, including manual construction withinthree-dimensional modeling software, procedural object creation, andthree-dimensional scanning of physical objects. Character model 200 canbe comprised of a set of polygons; voxels; higher-order curved surfaces,such as Bezier surfaces or non-uniform rational B-splines (NURBS);constructive solid geometry; and/or any other technique for representingthree-dimensional objects. Additionally, character model 200 can includeattributes defining the outward appearance of the object, includingcolor, textures, material properties, transparency, reflectivity,illumination and shading attributes, displacement maps, and bump maps.

Character model 200 is animated through armature 205. Armature 205includes one or more armature segments. In FIG. 2, the armature 205 areused to represent the pose of the upper arm of the character model 200.Animators manipulate the position and orientation of the segments ofarmature 205 to define a pose for the character model 200.

Armature segments can be constrained in size, position, or orientation,or can be freely manipulated by the animator. The number of armaturesegments can vary according to the complexity of the character, and atypical character can have an armature with hundreds or thousands ofsegments. In some cases, the number and position of armature segments issimilar to that of a “skeleton” for a character; however, armaturesegments can also define subtle facial expressions and other characterdetails not necessarily associated with bones or other anatomicalfeatures. Additionally, although the armature segments in the armature205 of FIG. 2 are comprised of a set of line segments, in alternateembodiments of the invention the armature segments can be comprised of aset of surfaces and/or a set of volumes.

Character model 205 is animated by creating a sequence of frames, orstill images, in which the character model 200 is progressively movedfrom one pose to another. Character model 200 can also be translated,rotated, scaled, or otherwise manipulated as a whole between frames.Animators can manually create the poses of a character model 200 foreach frame in the sequence, or create poses for two or more key frames,which are then interpolated by animation software to create the posesfor each frame. Poses can also be created automatically created usingfunctions, procedures, or algorithms.

Whether all or a portion of a pose is created manually by an animator orautomatically using a function, procedure, or algorithm, the pose ofcharacter model 200 can be defined by a set of animation variables. Onetype of animation variable specifies the rotation angles of an armaturesegment around an origin, referred to as a joint. In FIG. 2, the upperarm segment of armature 205 is rotated around joint 210. The rotation ofthe upper arm segment of the armature 205 around joint 210 is specifiedby animation variables 215, 217, 219, and 221. In this example, each ofthe animation variables 215, 217, 219, and 221 specifies a rotationabout a coordinate axis.

The position of points of character model 200 are determined, at leastin part, by model components 230. In an embodiment, animation variables225, which may include animation variables 215, 217, 219, and 221associated with joint 210, are input into the model components 230.Model components 230 then determines the position of one or more pointsof the character model 200 from the inputted animation variables. Modelcomponents 230 can employ any type of data processing function,procedure, or algorithm to determine the position of points of thecharacter model 200, including but not limited to simulations of skin,bone, fat and muscle layers; dynamic cloth simulations; sculpted shapes;metaballs; and physics simulations. Model components can be used todetermine the configuration of geometry or other attributes of charactermodel 200 for points on the surface of the character model, pointswithin the interior of character model 200, and/or points outside ofcharacter model 200.

In FIG. 2, model components 230 determine the position of points 240 and250 of character model 200. The output 235 of model components 230specifies the position of point 240. Similarly, the output 245 of modelcomponents 230 specifies the position of point 250. The positions ofpoints 240 and 250 can be specified by model components 230 in terms ofa displacement from the character model 200 in a base or rest position.

Alternatively, portions of the character model can be rotated inaccordance with nearby armature segments to form a geometrically posedcharacter model 260. A geometrically posed character model uses one ormore geometric operations to transform from a rest or unposedorientation to a posed orientation. Geometric operations includetranslation, scaling, rotation, and other similar manipulations ofportions of the character model, as well as the weighted or unweightedcombination of these operations. Geometric operations can also includeprojecting points of a character model from the surface of the charactermodel. The outputs 235 and 245 of model components 230 in turn specify afurther displacement of points 240 and 250 from their positions on thegeometrically posed character model 260. As discussed in detail below,regardless of how the model component specifies the position of pointson the character model, a baked component in conjunction with ageometrically posed character model can be used to approximate the modelcomponent.

The complexity of many types of model components makes posing acharacter model time-consuming and computationally expensive. Asdiscussed above, this hinders the ability of the animator to fine-tunecharacter animation to produce the desired drama and expression. Anembodiment of the invention optimizes the performance of modelcomponents by creating a statistical representation of each modelcomponent used to pose an character model. The statisticalrepresentation of the model component, referred to as a baked component,closely approximates the behavior of the model component with a greatlyreduced execution time. Furthermore, a baked component can be used toapproximate the behavior of any type of model component. Thus, the modelcomponents used to pose a character model can be replaced by equivalentbaked components, thereby improving execution performance and reducingthe computational resources needed in posing character models.

FIG. 3 illustrates the use of baked components to determine the posedposition of a point on an articulated character model according to anembodiment of the invention. Character model 300 is animated througharmature 305, which in FIG. 3 represents the pose of the upper arm ofthe character model 300. Animators manipulate the position andorientation of the segments of armature 305 to define a pose for thecharacter model 300.

The pose of character model 300 can be defined by a set of animationvariables, including animation variables 315, 317, 319, and 321, whichspecify the rotation of an upper arm segment of the armature 305 arounda joint 310. The position of points of character model 300 can bedetermined, at least in part, by model components 333. However, anembodiment of the invention decreases the execution time need to createa posed character model by replacing the model components 333 with acorresponding set of baked components 330 approximating the behavior ofthe model components 333. The baked components 330 are derived 334 fromthe model components 333. The baked components 330 can approximate anytype of data processing function, procedure, or algorithm to determinethe position of points of the character model 300, including but notlimited to simulations of skin, bone, fat and muscle layers; dynamiccloth simulations; sculpted shapes; metaballs; and physics simulations.

In an embodiment, the baked components 330 can be derived the modelcomponents 333 in advance of the posing of the character model 300.Further, once derived from the model components 333, the bakedcomponents 330 can be used repeatedly to determine multiple poses of acharacter model 300.

In an embodiment, animation variables 325, which may include animationvariables 315, 317, 319, and 321 associated with joint 310, are inputinto the baked components 330. Baked components 330 then determine theposition of one or more points of the character model 200 from theinputted animation variables 325.

In FIG. 3, baked components 330 determine the position of points 340 and350 of character model 300. The output 335 of model components 330specifies the position of point 340. Similarly, the output 345 of modelcomponents 330 specifies the position of point 350. The positions ofpoints 340 and 350 can be specified by model components 230 in terms ofa displacement from the character model 300 in a base or rest positionor alternatively as a displacement of points 340 and 350 from theirpositions on the geometrically posed character model 360.

As discussed above, baked components can be derived from modelcomponents prior to posing the character model. Additionally, once thebaked components have been computed, the character model can berepeatedly posed using the baked components. Thus, FIG. 4 illustratestwo phases of a method 400 for creating a posed character modelaccording to the embodiment of the invention. In the first phase 410,the baked components are derived from the model components in advance ofposing the character model. Following the creation of the bakedcomponents, a posed character model can be created using the bakedcomponents in the second phase 420. An embodiment of the invention canrepeat the second phase 420 to generate additional poses of thecharacter model without re-creating the baked components.

In an embodiment of the first phase 410, the baked components arecreated by analyzing the character model in set of training poses,referred to as a training set. FIG. 5 illustrates a method 500 forcreating a baked component from a model component associated with anarticulated character model according to an embodiment of the invention.

Step 505 identifies the set of animation variables and reference framesassociated with the model component. The identified animation variablesare the portion of the set of animation variables used to pose thecharacter model that are inputted to the model component. The referenceframes define regions of the character model affected by the outputs ofthe model component. In an embodiment, each reference frame defines alocal coordinate system for one or more armature segments and theadjacent portions of the character model. For the set of referenceframes associated with the model component, one frame is selected as aparent frame.

In an embodiment, a coordinate reference frame is composed of fourvectors: a first vector defining the origin or location of thecoordinate reference frame and three vectors defining the coordinateaxes of the coordinate reference frame. Each of the points of thecharacter model are associated with one or more reference frames via aset of reference frame weights. A set of reference frame weights definesa weighted average of the influence of the motion of one or morereference frames on a given point. In an embodiment, the associatedreference frames and animation variables are determined manually.Alternatively, an analysis of the model component can determine theanimation variables used as inputs and the set of points of thecharacter model, and hence the reference frames, potentially affected byits outputs.

FIGS. 6A–6C illustrate an example application of a method for creating abaked component from a model component associated with an examplearticulated character model according to an embodiment of the invention.FIG. 6A illustrates an example character armature 600 used in posing acharacter model 605. Armature 600 includes a number of reference frames,such as reference frame 607 associated with the lower right leg of thearmature 600 and reference frame 609 associated with the right shoulderof armature 600. Each reference frame is associated with one or morearmature segments and the adjacent portions of the character model 605.For example, reference frame 611 is associated with the torso region ofthe character model 605, reference frame 613 is associated with the leftshoulder area of the character model 605, and reference frames 615 and617 are associated with the upper and lower left arm, respectively, ofthe character model 605.

In step 505, the reference frames and animation variables associatedwith a model component are identified. For example, a muscle deformationmodel component used to determine the deformation of the arm ofcharacter model 605 may be associated with the set of reference frames611, 613, 615, and 617 and with the animation variables used to posearmature segments within these reference frames.

At step 510, the character model is posed according to a set of trainingposes. Each training pose is the result of the set of identifiedanimation variables set to example values. The set of training posesideally covers the normal range of motion for the portion of thecharacter model associated with the model component. In an embodiment,the number of poses in the training set corresponds to at least thenumber of different reference frames associated with the modelcomponent, if not more. In an embodiment, a typical character model mayhave a training set including several thousands poses.

In an embodiment, the points of the character model are geometricallyposed for each pose of the training set. The motion or posing ofportions of the character armature also moves the associated referenceframes. A geometric pose moves the points of the character modelaccording to the posed position of the associated reference frames,without any displacement from the model component. Step 510 records thevalues of the animation variables and the corresponding positions of thepoints of the character model potentially affected by the modelcomponent for each training pose. In an embodiment, the posed positionsof character model points is expressed in each of the set of referenceframes. The set of animation variable values and corresponding positionsof character model points comprises a set of sample data.

Continuing with the example of FIG. 6A, FIG. 6B illustrates an exampleset of training poses 620 for a set of reference frames and animationvariables associated with the left arm of a character model as calledfor by step 510. The training set 620 includes training poses 622, 624,626, 628, 630, and 632, each of which manipulates the portion of thecharacter model associated with the model component into a differentpose. In an example application of step 510, the values of the animationvariables and geometrically posed points of the character model for eachtraining pose are recorded to form a set of sample data.

Step 515 analyzes the set of sample data to determine an optimal set offrame basis functions. The portion of the set of set of sample dataexpressing the posed position of points is combined to form a matrix,and a single value decomposition of this matrix is calculated to find aset of frame basis functions for the set of sample data. In alternateembodiments, other methods of calculating a set of frame basisfunctions, such as a canonical correlation, can also be used. The set offrame basis functions can be used to express the position of modelpoints optimally in the sample set in a least squares sense. Determiningan optimal set of frame basis functions allows the set of sample data tobe expressed more compactly, thereby minimizing the amount of data to beanalyzed in subsequent steps of method 500. In an embodiment, step 515decomposes the set of sample data using the set of frame basis functionsto determine an optimized set of sample data. However, step 515 isoptional and an alternate embodiment of method 500 bypasses step 515 andperforms subsequent steps on the original set of sample data.

Step 520 determines a set of posing errors from the optimized set ofsample data. In an embodiment, posing errors for a given pose aredetermined by comparing the geometrically posed positions of the pointsof the character model with their corresponding positions output fromthe model component for the same set of animation variables. The posingerror for a character model point in a given pose is the differencebetween the position of the point output by the model component and thegeometrically posed position. In a further embodiment, the position ofpoints output from the model component changes over time. In thisembodiment, the posing error for a point in a given training pose is aseries of differences between the model component output over time andthe point's geometrically posed position. For each training pose in thetraining set, the posing error is determined for each point of thecharacter model potentially affected by the model component.

In another embodiment, the geometrically posed character model definesthe position of the “skin” of the character model. The model componentdefines a position of points relative to this skin. For example, a clothsimulation model component may define the position of points on acharacter model's clothing relative to the skin of the character model.In this embodiment, the geometrically posed character model defines thedirection or orientation of the posing error, and the output of themodel component defines a posing error along this orientation.

In an embodiment, the set of frame weights is used to represent theposing error for each point. The posing error for each point istransformed to the parent reference frame selected in step 505. From theparent reference frame, the posing error for each point is weightedaccording to the set of reference frame weights associated with thepoint and transformed from the parent reference frame to each referenceframe according to the frame basis functions determined in step 515. Bytransforming and distributing the posing error from the parent referenceframe to the other reference frames, the posing error associated witheach point of the character model will move with its associatedreference frames.

Continuing with the example of FIGS. 6A and 6B, FIG. 6C illustrates thedetermination of the posing error for an example training pose.Animation variables defining the training pose, including animationvariables 640, 642, 644, and 646, are input into the model component todetermine the posed character model 650. The position of points of thecharacter model, including points 652 and 654, are compared with theircorresponding positions on the geometrically posed character model 648.The posing errors 656 and 658 are the differences in positions betweenpoints 652 and 654, respectively, on the posed character model 650 andthe geometrically posed character model 648.

Step 525 analyzes the complete set of posing errors to determine thebaked component closely approximating the behavior of the modelcomponent. In an embodiment, a statistical regression analysis is usedto determine the posing error for the points of character model as afunction of the animation variables. In one implementation, a nonlinearquadratic regression analysis is performed on the set of posing errors.In this implementation, the animation variables are split into positiveand negative values, referred to as split animation variables, andconsidered as separate regression steps. In a further implementation, ifa positive split animation variable falls below zero, the value isclamped to zero. Similarly, a negative split animation is clamped tozero if it goes above zero. In a further embodiment, the split animationvariables, the square root of the split animation variables, and thesquare root of the product of adjacent split animation variables, whichare animation variables associated with the same joint, are all used inthe regression analysis to determine a function approximating the outputof the model component.

In a further embodiment, animation variables representing jointrotations are converted to a defrobulated form to prevent the appearanceof visual discontinuities. Unlike typical angle representations, thedefrobulated angles do not have any angular discontinuities within thenormal range of joint motion. In some applications, defrobulated anglestypically exhibit a higher degree of statistical correlation with theoutput of model components, for example due to defrobulated angleslacking gimbal lock and being continuous over the normal range of jointmotion. The conversion of joint angles from a four angle extended Eulerform to a corresponding defrobulated format is described in detail inthe related provisional and utility applications, “Defrobulation” and“Defrobulated Angles for Character Joint Representation”, 60/470,767 andSer. No. 10/844,049.

In summary of the defrobulated angle format, a joint rotationrepresented as a standard four angle rotation (tw, a, b, c),corresponding to the right-handed angle rotation form (x, y, z, x), isconverted to a set of projections xp=cos(a) cos(b); yp=cos(c)sin(a)+sin(c)sin(b)cos(a); and zp=sin(c) sin(a)−cos(c)sin(b)cos(a). Fromthe set of projections, xp, yp, and zp, a chord angle ch is defined asch=a cos(xp). The chord angle ch is used as an intermediate value todetermine a set of defrobulated angles (q, r, et). In an embodiment,q=ch*yp and r=ch*zp. The essential twist, et, is defined as:

${et} = {{tw} + {\arctan\left( \frac{zp}{yp} \right)} + {{\arctan\left( \frac{\sin(b)}{{\cos(b)}{\sin(a)}} \right)}.}}$

In its application to an embodiment of the present invention, animationvariables representing joint rotations and not already in defrobulatedform are converted into a defrobulated form as described above. Theregression analysis is then performed using the defrobulated form ofanimation variables. In a further embodiment, the defrobulated animationvariables are split into positive and negative values and considered asseparate regression steps. In addition, defrobulated animationvariables, their square roots, and the square roots of the products ofadjacent animation variables can be included in the regression analysis.

The baked component determined in method 500 can be used in place of themodel component in posing the character model for any desired pose,regardless of whether the desired pose was included in the training set.Furthermore, the output of several baked components can be combined todetermine the pose of all or one or more portions of a character model.

FIG. 7 illustrates a method 700 for determining the posed position ofpoints on an articulated character model from a baked componentaccording to an embodiment of the invention. For a desired charactermodel pose, which in an embodiment can be defined by a set of animationvariables, step 705 determines portion of the set of animation variablesassociated with the baked component. In an embodiment, the portion ofthe set of animation variables, referred to as the associated animationvariables, are those animation variable having a statistical correlationwith the output of baked component. Additionally, step 705 determinesthe reference frames associated with the baked component.

FIGS. 8A–8C illustrate an example application of a method fordetermining the posed position of a point on an articulated charactermodel from a baked component according to an embodiment of theinvention. In the example of FIGS. 8A–8C, the baked component representsthe operation of a muscle deformer used to determine the deformation ofthe left arm of character model for a desired pose. FIG. 8A illustratesthe selection of a set of reference frames associated with an examplebaked component for a desired pose as called for by an embodiment ofstep 705. Character armature 800 has been manipulated into a desiredpose according to a set of animation variables. Step 705 identifies aportion of the set of animation variables associated with the bakedcomponent. Additionally, the reference frames, such as reference frames805, 810, 815, and 820, affected by the baked component are alsoselected.

At step 710, the character model, or alternately the portions of thecharacter model potentially affected by the baked component, isgeometrically posed according to the associated animation variables.Character models can be geometrically posed in any manner known in theart.

FIG. 8B illustrates the determination of the geometrically posedpositions of points of the character model as called for by anembodiment of step 710. In FIG. 8B, step 710 poses the portion of thecharacter model 830 affected by the baked component according to theportion of the set of animation variables, including animation variables835, 840, 845, and 850. The result of the application of the portion ofthe set of animation variables is a geometrically posed character model855. Geometrically posed character model includes points 860 and 865.

Additionally, step 715 inputs the associated animation variables intothe baked component. For animation variables corresponding with jointangles, an embodiment converts the animation variables to a defrobulatedform to be input into the baked component. The output of the bakedcomponent is a posing error for at least one point on the charactermodel for the desired pose. In an embodiment, the baked componentoutputs a series of posing error values representing the posing errorover a period of time for at least one point on the character model.

If a set of optimal set of frame basis functions was used to reduce thesize of the set of sample data in creating the baked component, thenstep 720 applies the set of frame basis functions to the posing errorassociated with each point of the character model. As a result, theposing error is decomposed into its component values in the associatedreference frames.

Step 725 adds the posing error for each point to the position of thepoint on the geometrically posed character model and combines resultsinto a posed character model. The posed character model resulting fromthe use of the baked component closely approximates the result producedfrom the original model component for the same set of animationvariables.

FIG. 8C illustrates the application of posing errors output by the bakedcomponent to the geometrically posed positions of points of thecharacter model as called for by an embodiment of steps 715–725. Theportion of the set of animation variables 870 is input into the bakedcomponent 875 to produce a set of posing errors, including posing errors880 and 885. The set of posing errors used to displace points of thegeometrically posed character model, including points 860 and 865, tonew positions, such as 895 and 890, respectively. The new positions ofthe points of the character model closely approximate the positionsresulting from the application of the original model component.

It should be noted that once the posed or deformed model has beencreated using one or more of the above discussed embodiments, anyrendering technique, for example ray-tracing tracing or scanlinerendering, can create a final image or frame from the model incombination with lighting, shading, texture mapping, and any other imageprocessing information.

Further embodiments can be envisioned to one of ordinary skill in theart after reading the attached documents. In other embodiments,combinations or sub-combinations of the above disclosed invention can beadvantageously made. The block diagrams of the architecture and flowcharts are grouped for ease of understanding. However it should beunderstood that combinations of blocks, additions of new blocks,re-arrangement of blocks, and the like are contemplated in alternativeembodiments of the present invention.

The specification and drawings are, accordingly, to be regarded in anillustrative rather than a restrictive sense. It will, however, beevident that various modifications and changes may be made there untowithout departing from the broader spirit and scope of the invention asset forth in the claims.

1. A method of creating a baked component approximating the behavior ofa model component used to pose a character model, the method comprising:identifying at least a portion of the character model associated withthe model component; manipulating the character model through each of aset of training poses, wherein the set of training poses arerepresentative of a range of motion of the character model and definedby a set of inputs; determining a set of training posing errors from theset of training poses for at least one point of the character model,wherein each of the set of training posing errors is at least onedifference in position of the point of a character model from ageometrically posed position to at least one position specified by themodel component; and analyzing the set of training posing errors todetermine a relationship between the set of inputs and the set oftraining posing errors; wherein the set of inputs includes a set ofanimation variables and wherein a portion of the set of animationvariables are joint rotation angles expressed in a defrobulated form;and displaying the posted character model.
 2. The method of claim 1,wherein the portion of the character model associated with the modelcomponent is identified by at least one reference frame associated withthe model component and influencing the portion of the character model.3. The method of claim 1, wherein each of the set of training posingerrors is a series of differences in position over time of the point ofthe character model from the geometrically posed position to a set ofpositions over time specified by the model component.
 4. The method ofclaim 1, wherein the set of training posing errors is represented usinga set of basis functions determined from the training set.
 5. The methodof claim 1, wherein analyzing includes performing a regression analysisof the set of training posing errors against the set of inputs.
 6. Themethod of claim 5, wherein the set of inputs includes a set of animationvariables split into separate positive and negative valued variables. 7.A method of manipulating at least a portion of a character model into apose using a baked component, the, method comprising: identifying aportion of the character model associated with the pose; determining aset of geometrically posed positions of a set of points of the charactermodel from the pose; predicting a set of posing errors associated withthe set of points of the character model from the baked component andthe pose, wherein each of the set of posing errors specifies adisplacement of a point from a geometrically posed position; andapplying the set of posing errors to the set of geometrically posedpositions of the set of points; wherein the pose is defined at least inpart by a set of animation variables and wherein a portion of the set ofanimation variables are joint rotation angles expressed in adefrobulated form; and displaying the posed character model.
 8. Themethod of claim 7, wherein the portion of the character model associatedwith the pose is identified by at least one reference frame influencingthe portion of the character model.
 9. The method of claim 7, wherein atleast one of the set of posing errors specifies a series ofdisplacements of a point from a geometrically posed position over time.10. The method of claim 7, wherein applying the set of posing errorsincludes transforming each of the set of posing errors into a set ofreference frames associated with a set of basis functions.
 11. Themethod of claim 10, wherein the set of basis functions is determinedfrom a training set.
 12. A method of manipulating at least a portion ofa character model into a pose using a model component, the methodcomprising: creating a baked component from the model component;identifying a portion of the character model associated with the bakedcomponent; determining a set of geometrically posed positions of a setof points of the character model from the pose; predicting a set ofposing errors associated with the set of points of the character modelfrom the baked component and the pose, wherein each of the set of posingerrors specifies a displacement of a point from a geometrically posedposition; and applying the set of posing errors to the set ofgeometrically posed positions of the set of points; wherein the pose isdefined at least in part by a set of animation variables and wherein aportion of the set of animation variables are joint rotation anglesexpressed in a defrobulated form; and displaying the posed charactermodel.
 13. The method of claim 12, wherein the portion of the charactermodel associated with the pose is identified by at least one referenceframe influencing the portion of the character model.
 14. The method ofclaim 12, wherein at least one of the set of posing errors specifies aseries of displacements of a point from a geometrically posed positionover time.
 15. The method of claim 12, wherein creating the bakedcomponent from the model component comprises: identifying at least aportion of the character model associated with the model component;manipulating the character model through each of a set of trainingposes, wherein the set of training poses are representative of a rangeof motion of the character model and defined by a set of inputs;determining a set of training posing errors from the set of trainingposes for at least one point of the character model; and analyzing theset of training posing errors to determine a relationship between theset of inputs and the set of training posing errors.
 16. The method ofclaim 15, wherein the portion of the character model associated with themodel component is identified by at least one reference frame associatedwith the model component and influencing the portion of the charactermodel.
 17. The method of claim 15, wherein the set of inputs includes aset of animation variables.
 18. The method of claim 17, wherein aportion of the set of animation variables are joint rotation anglesexpressed in a defrobulated form.
 19. The method of claim 15, whereineach of the set of training posing errors is at least one difference inposition of the point of a character model from a geometrically posedposition to at least one position specified by the model component. 20.The method of claim 19, wherein each of the set of training posingerrors is a series of differences in position over time of the point ofthe character model from the geometrically posed position to a set ofpositions over time specified by the model component.
 21. The method ofclaim 15, wherein the set of training posing errors is represented usinga set of basis functions determined from the training set.
 22. Themethod of claim 15, wherein analyzing includes performing a regressionanalysis of the set of training posing errors against the set of inputs.23. A computer-readable medium having stored thereon a plurality ofinstructions, when executed by a computer, causes the computer device toperform an operation comprising the steps of: creating a baked componentfrom a model component; identifying a portion of a character modelassociated with the baked component; determining a set of geometricallyposed positions of a set of points of the character model from a pose;predicting a set of posing errors associated with the set of points ofthe character model from the baked component and the pose, wherein eachof the set of posing errors specifies a displacement of a point from ageometrically posed position; and applying the set of posing errors tothe set of geometrically posed positions of the set of points; whereinthe pose is defined at least in part by a set of animation variables andwherein a portion of the set of animation variables are joint rotationangles expressed in a defrobulated form.
 24. The computer-readablemedium of claim 23, wherein the portion of the character modelassociated with the pose is identified by at least one reference frameinfluencing the portion of the character model.
 25. Thecomputer-readable medium of claim 23, wherein at least one of the set ofposing errors specifies a series of displacements of a point from ageometrically posed position over time.
 26. The computer-readable mediumof claim 23, wherein creating the baked component from the modelcomponent comprises: identifying at least a portion of the charactermodel associated with the model component; manipulating the charactermodel through each of a set of training poses, wherein the set oftraining poses are representative of a range of motion of the charactermodel and defined by a set of inputs; determining a set of trainingposing errors from the set of training poses for at least one point ofthe character model; and analyzing the set of training posing errors todetermine a relationship between the set of inputs and the set oftraining posing errors.
 27. The computer-readable medium of claim 26,wherein the portion of the character model associated with the modelcomponent is identified by at least one reference frame associated withthe model component and influencing the portion of the character model.28. The computer-readable medium of claim 26, wherein the set of inputsincludes a set of animation variables.
 29. The computer-readable mediumof claim 28, wherein a portion of the set of animation variables arejoint rotation angles expressed in a defrobulated form.
 30. Thecomputer-readable medium of claim 26, wherein each of the set oftraining posing errors is at least one difference in position of thepoint of a character model from a geometrically posed position to atleast one position specified by the model component.
 31. Thecomputer-readable medium of claim 30, wherein each of the set oftraining posing errors is a series of differences in position over timeof the point of the character model from the geometrically posedposition to a set of positions over time specified by the modelcomponent.
 32. The computer-readable medium of claim 26, wherein the setof training posing errors is represented using a set of basis functionsdetermined from the training set.
 33. The computer-readable medium ofclaim 26, wherein analyzing includes performing a regression analysis ofthe set of training posing errors against the set of inputs.